"She has a good forehand with a big spin and quite fast on the backhand," Kvitova said of Errani. "I think that it will be a tough match tomorrow."

Kvitova broke Wozniacki twice in both sets, including in the Dane's last service game in the second.

"I didn't feel like I had many chances," Wozniacki said. "She just went for every shot and hit it deep and I came under pressure straightway."

Wozniacki converted just one of her five break points and won only 54 percent of points on her first serve compared to 70 percent for Kvitova.

The Czech said she is feeling much better than this time last season, when she was struggling with injuries. She has a chance to move up to No. 7 in the rankings if she wins the tournament.

Errani and Vinci, the world's top doubles pair, are good friends off the court. Both players struggled to hold serve in a match with a total of 11 breaks, with Errani improving her record to 5-2 against Vinci.

"It's very tough because we know each other very well," Errani said. "It's tough to play against one person and know what you're going to do in every shot."

Errani reached the final of the Open GDF Suez this month but lost to unseeded Mona Barthel of Germany.